Quote Originally Posted by andrew mcgregor View Post
Nova robotics - thanks for the excellent calculations. I’d done some of the same myself but I have more confidence in your numbers.

Based on your calculations with 150mm ducting and a duct velocity of 29.3 m/s, using Hemjo’s table it looks to me like that velocity will accommodate all or most activities in my wood workshop - in many cases with reasonable head room. Or am I missing something in that simple interpretation eg losses due to various factors?

Regards

Andrew
That's average velocity within the duct. Boundary layer effects mean the air velocity near the walls of the duct are much slower, and around elbows and other features you'll find all kinds of dead air. If you're getting near those velocities you're going to accumulate little deposits of crud all throughout your ductwork. Imagine how bad the hose on your vacuum cleaner would get if you turned the speed of the motor all the way down to the point where it would just barely lift dust. That's the situation you're trying to avoid.